Substituent constants and regression analysis are being employed to formulate quantitative structure-activity relationships with organic compounds interacting with biomedicinal chemical systems. The formulated equations, the data upon which they are based, and the chemical structures in WLN notation are stored for computer manipulation and study. The goal of this work is to develop a truly general system for computerized drug development and design. It is also planned to determine more octanol/water partition coefficients on compounds of interest in biomedicinal chemistry. To better understand the interactions of ligands with macromolecules, the interaction of a few carefully designed sets of congeners with enzymes will be undertaken. Dihydrofolate reductase and papain seem to be particularly worthy of study, the former because of its importance in cancer chemotherapy, the latter because of the detailed knowledge of its structure and reactivity. BIBLIOGRAPHIC REFERENCES: C. Silipo and C. Hansch, Il Farmaco Ed. Sci. 30, 35 (1975). The Structure-Activity Relationship of 9-(X-Phenyl)guanine Inhibitors of Xanthine Oxidase. M. Yoshimoto, C. Hansch, and P. Y. C. Jow, Chem. Pharm. Bull. 23, 437 (1975). Structure-Activity Relationships in Immunochemistry. III. Inhibition of Complement by Benzylpyridinium Ions.